It is often necessary to introduce treatment chemicals into fluid producing wells in order to correct or prevent certain undesirable conditions. Corrosion or scale inhibitors, for example, have been introduced in a variety of ways in both solid and liquid form. One method of introduction involves pumping or pouring chemicals in liquid form down the tubing string or the production string, or through separate strings of tubing inserted into the well bore for that purpose. Although chemicals in liquid form can be readily mixed with the flow of production fluids and can be readily pumped or poured at controlled rates, there are serious disadvantages to the use of these treatment methods. The use of additional strings of tubing is expensive and runs the risk of interfering with other operations of the well, while the pumping or pouring of liquid chemicals from the surface down into the well can require an excess of chemicals to be introduced, at a correspondingly higher cost, in order to ensure adequate distribution throughout the well.
Both solid and liquid treatment compositions have also been introduced from containers which are filled with chemicals on the surface and lowered into the well. A number of ways have been suggested for introducing chemicals into the production fluid from containers, one of which is through use of containers which are degradable by the treatment composition or by the well fluid. While overcoming some of the objections to the continuous pumping or pouring of liquid chemicals referred to above, there are distinct disadvantages to this approach as well. Some methods of introducing the containers and releasing the chemicals require temporary interruption of well production, while most methods of chemical release are not able to continuously inject controlled amounts of treatment chemicals into the production fluid over an extended period of time. The result has been the introduction of chemicals basically in the form of a batch treatment process of short duration, with less control over the operation than desired. Moreover, the amount of chemicals which can be introduced by containers is limited to the size container that can fit into the lubricator.
Another way of introducing liquid treatment chemicals involves the use of containers which incorporate various types of mechanical arrangements for causing the release of chemicals carried by the containers. For example, pistons, bellows, pumps and the like have been incorporated in containers for injecting or pumping treatment liquid into the well. While enabling some control over the rate at which the liquid is introduced, these mechanical arrangements are generally relatively complicated in design, resulting in costly containers, a higher probability of failure than desired and a relatively short operating life.
It would be desirable to be able to introduce chemical treatment fluids into a well bore in a simpler, less complicated manner which does not have the objectionable characteristics mentioned above and yet which is accurate, reliable, and inexpensive to install and operate. It would also be desirable to be able to introduce chemicals from a container or chamber having far greater storage capacity than that of conventional containers. Further, it would be highly desirable to be able to accomplish the foregoing objects of the invention with a system which can introduce treatment fluids over a relatively long period of time.